As one of high-speed Field effect transistors (FETs) with excellent breakdown tolerance, there is a field effect transistor using a gallium nitride (GaN) based semiconductor material having wide-bandgap characteristics. The field-effect transistor using GaN is used for, for example, a high-frequency amplifier, a high power amplifier, and a power switching device. However, it is difficult to fabricate a GaN substrate for epitaxial growth of such a structure, thus in many cases, GaN is epitaxially grown on an SiC substrate, sapphire substrate, and an Si substrate, for example. At this time, an abnormal growth portion may be generated on the surface of a GaN epitaxial film depending on a substrate used for growing GaN and growth conditions.
Possible causes of forming an abnormal growth portion 103 are a defect (micropipe) in an SiC substrate 101 where a GaN film 102 is grown and abnormal growth around a minute dust adhered during the growth. The abnormal growth portion could be formed on a GaN film that is epitaxially grown on an Si substrate and a sapphire substrate and on an SiC film that is epitaxially grown on an SiC substrate.
Patent Literature 1 discloses a technique relating to a high power transistor that is capable of reducing drain-to-source capacitance by dividing a drain electrode into two. Moreover, Patent Literature 2 discloses a technique in which drain electrodes and source electrodes are formed in lattice to reduce parasitic capacitance in the drain electrodes and the source electrodes.